The present invention relates to a metal sheet ventilation/smoke exhaust duct section being a part of a metal sheet ventilation/smoke exhaust duct, where the metal sheets are covered on the outside by a heat insulating material and where the duct section includes elongated stiffening bar members located on the outside of the duct, attached to the metal sheets.
Fire regulations require that a tight seal be established in the area where the section of the ventilation/smoke exhaust duct passes through a fire rated wall such that flames and/or toxic gases largely will not pass from one building area to the adjoining building area in case of fire in one of the areas. DIN 4102 Part 4 requires the provision of vertical internal stiffening pipes and, as the case may be, a round-going stiffening frame made up from an L-shaped profile with one leg lying flatly against the metal sheet outer surface. The mounting of the aforementioned vertical pipes inside the duct is time-consuming and also restricts the free flow of air through the ventilation/smoke exhaust duct in normal operation. Moreover, it has been found that the aforementioned stiffening L-shaped frame often applied may in fact in certain cases bring about a further loss of seal between the duct section and the wall.